Repair method for noise suppression structure

ABSTRACT

A method is provided for repairing a defect in a noise suppression panel. The method may be used to repair defects in a panel that may occur during the manufacture of or normal use of the panel. The method includes the steps of removing the defect from the noise suppression panel to create a cavity therein, forming material comprised of a material having acoustic damping properties into an insert configured to mate with the cavity, and placing the insert into the cavity.

FIELD OF THE INVENTION

The present invention relates to noise suppression structures and, more particularly, to noise suppression structures for aircraft ducts and plenums, and methods of repairing the structures.

BACKGROUND OF THE INVENTION

Many aircraft are powered by jet engines. In most instances, jet engines include one or more gas-powered turbine engines, auxiliary power units (APUs), and/or environmental control systems (ECSs), which can generate both thrust to propel the aircraft and electrical energy to power systems installed in the aircraft. Although most aircraft engines are generally safe, reliable, and efficient, the engines do exhibit certain drawbacks. For example, the turbine engines, as well as other components that make up the engine, can be sources of unwanted noise, especially during aircraft take-off and landing operations. Moreover, APUs and ECSs can be sources of unwanted ramp noise. Thus, various governmental rules and regulations aimed at mitigating such noise sources have been enacted.

To address, and at least somewhat alleviate, the unwanted noise emanating from aircraft noise sources, and to thereby comply with the above-noted rules and regulations, various types of noise reduction treatments have been developed. For example, one type of noise reduction treatment that has been developed for use in aircraft ducts is a noise suppression panel. In many instances, noise suppression panels are flat or contoured, and include a honeycomb structure disposed between a backing plate and a face plate. Other noise suppression materials and structure may also be disposed between the backing plate and face plate. The noise suppression panels are typically placed on the interior surface of engine or APU inlet and/or outlet plenums, as necessary, to reduce noise emanations.

Periodically, these noise suppression panels may become damaged from normal wear. Voids may form in the panel, or alternatively, air gaps between the face plate and honeycomb structure may appear. Conventionally, the repair of these damaged sections include, for example, applying liquid resin to the voids or air gaps and subsequent curing of the panel. Other repair methods have included filling the voids or damaged sections with a clay-like substance. However, neither cured resins nor clay have acoustic damping properties, and thus, can reduce, rather than maintain or enhance, the noise suppression capabilities of the panel.

The foam core material in the noise suppression panels may contain manufacturing defects, such as voids or uneven surfaces. In these cases, the defective panels may not operate as intended and have historically been entirely discarded. As a result, the costs of aircraft manufacture and/or maintenance may increase.

Hence, there is a need for a method of repairing a noise suppression panel that restores the noise suppression capabilities of the panel to its original specifications, and/or is less costly compared to known methods, and/or maintains noise suppression capabilities over a relatively wide frequency range. The present invention addresses one or more of these needs.

SUMMARY OF THE INVENTION

A method is provided for repairing a defect in a noise suppression panel.

In one embodiment, and by way of example only, first, a section of the noise suppression panel that includes the defect is removed to thereby create a cavity in the panel. Next, an insert configured to mate with the cavity is formed from a material having acoustic damping properties. Then, the insert is placed at least partially within the cavity.

In another exemplary embodiment, a method is provided for repairing a defect in a noise suppression panel having a back plate, a face plate and a bulk absorber disposed therebetween. The method includes removing at least a portion of the face plate, removing a section of the noise suppression panel that includes the defect to thereby create a cavity in the panel, forming an insert configured to mate with the cavity from a material having acoustic damping properties, placing the insert into the cavity, and bonding the insert to the back plate.

Other independent features and advantages of the preferred method will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified perspective view of a noise suppression panel according to an exemplary embodiment of the present invention;

FIG. 2 is a perspective view of an exemplary damaged noise suppression panel;

FIG. 3 is a perspective view of another exemplary damaged noise suppression panel;

FIG. 4 is a simplified schematic representation of one step of an exemplary process for repairing the noise suppression panel of FIGS. 1-3, according to one embodiment of the present invention;

FIG. 5 is a simplified schematic representation of another step of an exemplary process for repairing the noise suppression panel of FIGS. 1-3, according to one embodiment of the present invention;

FIGS. 5A and 5B are cross sectional views of the noise suppression panel illustrated in FIG. 5 taken along lines 5A, 5B-5A, 5B;

FIG. 6 is a simplified schematic representation of yet another step of an exemplary process for repairing the noise suppression panel of FIGS. 1-3, according to one embodiment of the present invention;

FIG. 6A is an exemplary insert that may be used in the step depicted in FIG. 6;

FIG. 6B is another exemplary insert that may be used in the step depicted in FIG. 6;

FIG. 7 is a simplified schematic representation of still yet another step of an exemplary process for repairing the noise suppression panel of FIGS. 1-3, according to one embodiment of the present invention;

FIGS. 7A and 7B are cross sectional views of the noise suppression panel illustrated in FIG. 7 taken along lines 7A, 7B-7A, 7B; and

FIG. 8 is a flowchart of an exemplary process for repairing the noise suppression panel of FIGS. 1-3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Before proceeding with the detailed description, it is to be appreciated that the described embodiment is not limited to use in conjunction with a particular type of engine, or in a particular type of vehicle. Thus, although the present embodiment is, for convenience of explanation, described as being implemented in an aircraft environment, it will be appreciated that it can be implemented in various other types of vehicles, and in various other systems and environments.

Turning now to the description, and with reference first to FIG. 1, an exemplary noise suppression panel 100 is depicted in perspective and cross section, respectively. In FIG. 1, the panel 100 includes a back plate 102, a face plate 104, and a bulk absorber 106. The back plate 102 is preferably imperforate and is constructed of any one of numerous types of non-porous materials such as, for example, aluminum, epoxy, or bismaleimide (BMI). As will be described more fully below, the back plate 102 is preferably bonded directly to the bulk absorber 106 during manufacture of the panel 100.

The face plate 104 is constructed of any one of numerous types of materials such as, for example, aluminum, and carbon composites. In one exemplary embodiment, the face plate 104 is constructed of BMI, and is perforated to a desired percent open area (POA) value. As is generally known, relatively low POA values (e.g., ˜5%) provide acoustic resistance, whereas relatively high POA values (e.g., ˜30%) provide acoustic transparency. In a particular preferred embodiment, the face plate 104 is perforated to a POA value greater than 30% to ensure the face plate 104 is acoustically transparent to any incident sound. In another exemplary embodiment, the face plate 104 is a screen. Similar to the back plate 102, and as will be described further below, the face plate 104 is also preferably bonded to the bulk absorber 106 during manufacture of the panel 100.

The bulk absorber 106 is disposed between the back plate 102 and face plate 104 and, as was mentioned above, is preferably directly bonded to each plate 102, 104 during manufacture of the panel 100. The bulk absorber 106 may be constructed of any one of numerous materials, such as, for example, foamable material, material having honeycomb cavities therein, honeycomb material filled at least partially with epoxy for structural enhancement, or any one of numerous other type of acoustic damping material. In one exemplary embodiment, the bulk absorber 106 is an open cell foam bulk absorber, such as the type disclosed in U.S. patent application Ser. No. ______ entitled “Noise Suppression Structure Manufacturing Method” filed on May 20, 2004 and U.S. patent application Ser. No. ______ entitled “Noise Suppression Structure and Method of Making Same” filed on Feb. 20, 2004.

Occasionally, during manufacture or as a result of normal wear, the noise suppression panel 100 may become damaged or defective. The damage may take any one of numerous forms. For example, and as shown more clearly in FIG. 2, the bulk absorber 106 may include a void 202 that adversely affects the noise suppression capabilities of the noise suppression panel 100. The void 202 may extend partially or entirely through the thickness of the bulk absorber 106. Although the void 202 is illustrated as being proximate a corner of the panel 100, it will be appreciated that the damage may occur at various locations on the panel 100. For instance, the damage may be present on the edge of a panel 100, such as a void 204 illustrated in FIG. 2. The defect may be a shallow depression with a skin at the surface of the bulk absorber. This type of defect may result from incomplete filling of the mold during the manufacturing process. In another example, the defect may be a density defect 206, which may result when the density of one section is higher or lower than desired. In other cases, the back plate 102 and/or face plate 104 may be damaged. As illustrated in FIG. 3, the face plate 104 may pull apart from the bulk absorber 106 or a void 208 may appear in the bulk absorber 106.

Regardless of the particular type of defect, the bulk absorber 106 is preferably repaired and the repair method of the present invention is preferably employed. The overall process 500 is illustrated in FIGS. 4-8, and will first be described generally. It should be understood that the parenthetical references in the following description correspond to the reference numerals associated with the flowchart blocks shown in FIG. 8. First, the defect 402 on the bulk absorber 106 is removed to create a cavity 404 (510). Next, acoustic damping material 406 is formed into an insert 408 that is configured to mate with the cavity 404 (520). The insert 408 is then placed into the cavity 404 (530). In an alternative embodiment, the insert 408 is bonded to the cavity 404 (540). These steps will now be discussed in detail below.

As briefly mentioned previously and as shown in FIGS. 4 and 5, the defect 402 is removed from the bulk absorber 106 to create a cavity 404 (510). The cavity 404 is preferably sized larger than the defect 402 and may be created in any one of numerous manners. Any one of numerous shapes may be machined into the bulk absorber 106. In one exemplary embodiment, a circular saw is employed to cut the defect 402 out of the bulk absorber 106. As a result, the cavity 404 created has a circular shape. In another exemplary embodiment, the bulk absorber 106 is attached to the backing plate 102, thus, the cavity 404 is formed without damaging the backing plate 102. In yet another exemplary embodiment, the defect 402 is removed with a contoured cutting tool and a cavity 404 having a predetermined shape is formed in the bulk absorber 106. At least a portion of the cutting tool may be covered with an abrasive, such as diamond dust, so that the walls of the cavity 404 may be smooth.

In some instances, the shape of the cavity walls 410 may provide an improved surface to which a repair may be made. For example, the cavity walls 410 may have a beveled (as illustrated in FIG. 5A), stepped (as illustrated in FIG. 5B), or threaded shape. Threaded walls may be used for threading the insert 408 into the cavity 404 and for providing additional surface area for bonding. In another exemplary embodiment, a flowable material, such as epoxy, is applied to the cavity walls 410 and hardens to reinforce the cavity walls 410. The reinforced cavity walls 410 may be used to provide an improved surface to which to bond.

With reference to FIG. 6, once the defect 402 is removed, an insert 408 is then formed from acoustic damping material 406 (520). The insert 408 is preferably configured to tightly fit in the cavity 404. In another exemplary embodiment, the insert 408 is sized slightly larger than the cavity 404. In yet another exemplary embodiment, the insert 408 has a thickness that is slightly greater than the bulk absorber 106. In still yet another embodiment, the cavity walls 410 have a beveled, stepped, or threaded shape. Accordingly, the insert walls 412 are configured to have a shape that mates with the beveled or stepped shape, such as shown in FIGS. 6A and 6B, respectively.

The insert 408 can be formed by any one of numerous methods. Some examples include, but are not limited to machining, cutting, or chiseling the insert 408 out of the material 406. Any one of numerous tools, such as a straight circular saw or a hole cutter with beveled walls may be used to form the insert 408 from the material 406. As those with skill in the art may appreciate, tools used for forming the insert 408 and tools for creating the cavity 404 may be matched sets having a variety of graded cutter sizes that may be useful to cover the expected range of defect sizes.

It will additionally be appreciated that the acoustic damping material 406 may be any one of a number of materials that suitably suppress noise to a predetermined noise level. Preferably, the acoustic damping material 406 damps aircraft noise by between about 5 and 10 dB, however, as appreciated by those skilled in avionics, the acoustic damping material 406 most preferably meets federal noise level standards mandated by the Federal Aviation Administration. Examples of suitable materials include but are not limited to, the bulk absorber 106 materials mentioned above, conventional honeycomb treatments, and those materials disclosed in U.S. patent application Ser. No. ______ entitled “Noise Suppression Structure Manufacturing Method” filed on May 20, 2004, and U.S. patent application Ser. No. ______ entitled “Noise Suppression Structure and Method of Making Same” filed on Feb. 20, 2004.

The acoustic damping material 406 can be the same material from which the bulk absorber 106 is manufactured. However, this is not a requirement; accordingly, the acoustic damping material 406 and bulk absorber 106 material may be different materials. In one exemplary embodiment, the acoustic damping material 406 has mechanical properties that are at least comparable to those of the bulk absorber 106 material to maintain the mechanical integrity of the bulk absorber 106.

Turning now to FIG. 7, once an appropriate insert 408 is formed, the insert 408 is placed in to the cavity 404 such that the cavity walls 410 and insert walls 412 mate with one another (530). In some embodiments, and as was mentioned above, the cavity walls 410 and insert walls 412 each have beveled or stepped shapes that mate with one another and mechanically lock the insert 408 into the cavity 404, such as illustrated in FIGS. 7A and 7B, respectively.

As previously mentioned, in an alternative embodiment, the insert 408 is bonded to the cavity 404 (540). Any known bonding method and bonding agent may be implemented. For example, a bonding agent, such as any one of numerous glues, epoxies, silicone adhesives, or ceramic cements may be applied to the cavity walls 410, insert walls 412, or both. After the insert 408 and cavity 404 are aligned and brought into contact with one another, pressure is applied and maintained on the bonded area until the bonding agent has set. In an exemplary embodiment, after the insert 408 is inserted into the cavity 404, the top and bottom surfaces of the bulk absorber 106 panel around the insert 408 are machined down to create a uniform surface. In another exemplary embodiment, bonding may be employed in conjunction with mechanically locking the insert 408 into the cavity 404.

In the case where the repair process is performed on a noise suppression panel 100 having a back plate 102, a face plate 104, and bulk absorber 106, the face plate 104 first is removed (550). Then, the defect 402 is removed from the bulk absorber 106 without damaging the back plate 102. After the cavity 404 is prepared to receive the insert 408, the insert 408 is bonded at least to the back plate 102.

When the repair process is performed on a bulk absorber 106 panel during manufacture, after the bulk absorber 106 is repaired, a back plate 102 is bonded to the bulk absorber 106. Alternatively, a face plate 104 may be bonded to the bulk absorber 106 as well.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A method for repairing a defect in a noise suppression panel, the method comprising: removing a section of the noise suppression panel that includes the defect to thereby create a cavity in the panel; forming an insert configured to mate with the cavity from a material having acoustic damping properties; and placing the insert at least partially within the cavity.
 2. The method of claim 1, wherein the cavity and the insert each have a sidewall and the method further comprises: applying a bonding agent to at least one of the sidewalls; and adhering the insert sidewall and cavity sidewall to one another.
 3. The method of claim 2, wherein the bonding agent comprises one of epoxy, silicone adhesive, and ceramic cement.
 4. The method of claim 1, wherein the cavity and insert are each cylindrically-shaped.
 5. The method of claim 1, wherein the cavity and insert are each beveled.
 6. The method of claim 1, wherein the cavity and insert are each stepped.
 7. The method of claim 1, wherein the cavity and insert are each threaded.
 8. The method of claim 1, wherein the panel comprises a back plate, the method further comprising: bonding the insert to the back plate.
 9. The method of claim 1, wherein the defect is removed by, and the insert is formed using, a circular saw.
 10. The method of claim 1, wherein the defect is removed from the panel using a contoured cutting tool.
 11. The method of claims 1 further comprising machining threads into the cavity and insert.
 12. The method of claim 1, wherein the noise suppression panel and acoustic damping material are the same material.
 13. The method of claim 12, wherein the acoustic damping material comprises one of an open cell foam bulk absorber material and a high temperature honeycomb material.
 14. The method of claim 1, wherein the noise suppression panel has a first and a second side, the method further comprising: bonding a back plate to the first side of the noise suppression panel.
 15. The method of claim 14, wherein the back plate comprises a non-porous material.
 16. The method of claim 14, further comprising: bonding a face plate to the second side of the noise suppression panel.
 17. The method of claim 16, wherein the face plate comprises a material that is perforated to a percent open area (POA) value greater than 30%.
 18. The method of claim 16, wherein the face plate comprises a screen.
 19. A method for repairing a defect in a noise suppression panel having a back plate, a face plate and a bulk absorber disposed therebetween, the method comprising: removing at least a portion of the face plate; removing a section of the noise suppression panel that includes the defect to thereby create a cavity in the panel; forming an insert configured to mate with the cavity from a material having acoustic damping properties; placing the insert into the cavity; and bonding the insert to the back plate.
 20. The method of claim 19, wherein the acoustic damping material comprises one of an open cell foam bulk absorber material and a high temperature honeycomb material.
 21. The method of claim 19, wherein the bulk absorber and acoustic damping material are the same material. 